Here's an idea, horse armor enchantments which increases it's ability. got horses but they aren't worth while? enchant some armor for them and give them a speed boost and a jump boost to tackle those tall mountains. Ay? sounds good, simple idea which makes people want to use horses.
If we didn't have a terrible custom terrain I would disagree. But with these mountains and hills it might be a good idea. Really pointless though. I mean, who uses horses in factions?